Bachmann Gordon HO/OO scale

[Matthew1991]

Hello,
I have a Bachmann Gordon in the HO/OO scale and his tender bounces and details when he goes over the points on our track.

Having done some experiments with weights with no success we have discovered that it only occurs when he is pulling anything. While pushing or running solo the tender doesn't move but with carriages attached it bounces over the two sets of points on our line and details.
Has anyone has something similar or have any suggestions for a fix?

Thanks